Effect of neutral salt spray (NSS) exposure on the lap-shear strength of adhesive-bonded 5052 aluminum alloy (AA5052) joints

This work explores the mechanisms for the non-linear degradation of the lap-shear strength of adhesive-bonded 5052 aluminum alloy (AA5052) joints exposed to neutral salt spray (NSS) environment up to 1200 hours. The lap-shear testing results show that a mixed failure dominated by adhesive failure occurred in both unexposed and exposed adhesive-bonded AA5052 joints. The lap-shear strength of adhesive-bonded AA5052 joints declined sharply in the preliminary stage of NSS exposure (e.g. shorter than 240 hours), then it decreased moderately as the NSS exposure time increased. Differential scanning calorimetry (DSC), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electrochemical noise measurement were applied to exploring the degradation mechanisms of the lap-shear strength of adhesive-bonded AA5052 joints. The adhesive properties remained nearly unchanged after exposure in the NSS environment. The decreased hydrogen bond at the AA5052/adhesive interface was responsible for the sharp degradation of the lap-shear strength of adhesive-bonded AA5052 joints in the preliminary stage of NSS exposure. In the later stage of NSS exposure (e.g. more than 240 hours), the surface oxidation of AA5052 substrates dominated the lap-shear strength degradation of adhesive-bonded AA5052 joints.